hartz killed my cat

I used the flea and tick drops on both of my cats. within hours they were both lethargic. one wouldn’t leave the bathtub and the other would leave the counter. after 3 days of this i woke to find my cat in the bathtub dead. she was only 5. mt older cat who was very heavy lost all of her body weight she looks like a skeleton i am trying very hard to get her to gain weight. i am afraid she will die too. I called hartz and they did not care at all. their products killed the love of my life i can never forgive them for this.